Electrical heating element



Jan. 11 Q 1927. 1,614,330

E. L. WlEGAND ELECTRICAL HEATING ELEMENT Filed Augflst 31, 1923 4Sheets-Sheet l 00o oooooooooooooo 00o ooooooooooooooooooooooooooooooooooo ooooooooooooooooooo ooooooooooooooooooooooooooooooooooooooo ooooooooooooo'oooooo ag/M 00000000 0000 ooooooooo00000 0000000070 00000 000000000 00000 000000000 0001000000 000000000000000000 000000000 000000000 000000000 000000000 0000000 00000000000000 000000000 0000000 0000000 0000000 00000000 00000000 00000000000000 0000000 00000000 00000000 00000000 4 Sheets-Sheet 2' E. L.WIEGAND ELECTRICAL HEATING ELEMENT Filed August 31, 1923 Jan. 11 1927.

j {zrrx7 v 1,614,330 11 1927' E. LQWIEGAND ELECTRICAL HEATING ELEMENTFiled August 31 1925 4 Sheets-Sheet a Jan.'11,1927. 1,614,330 v E. L.WlEGAND I ELECTRICAL HEATING ELEMENT 4 Sheets-Sheet 4 Filed August 51,1923 resistor temperature.

Patented Jan. 11, 1927.

PATENT OFFICE.

EDW IN L. WIEGAND, OF DOBHONT BOROUGH, PENNSYLVANIA.

nns-crates; naa'rnre ELEMENT.

Application filed August 81, 1923. Serial 1%.660384.

This invention relates to new and useful improvements in electricalheating elements of the type wherein the resistor is enveloped inrefractory material. .More specifically the invention maybe stated'toconsist of a novel class of heating elements and a process for makingthe same wherein. the

resistor is enveloped in a sheet metal casing.

and insulated therefrom by a compact mass of refractory material.

I am aware that aresistor in the form of a single straight conductor hasbeen onclosed in a metal sheath and insulated there from by finely'divided refractory material-,- such a construction being commonlyreferred to as sheathed wire. This type of heating element has thedisadvantage that it is very difficult and expensive to manufacture.During the drawing process, the

resistor wire develops irregularities in cross.

section andhence the life oftheelement is greatly shortened. Therefractory material also becomes unevenly displaced, and the resistorisnot located centrally with respect to the outer metal casingand'therefore the insulation is impaired. This sheath wire is capable ofbeing bent and massed into spiral and serpentine forms of heatingelements with some degree of success, although it will be obvious thatthereis adouble wall of .the refractory material and metal casingbetween each convolution or adjacent length of the spiral or serpentine'type of heating element. This double wall requires space'that mightwell be utilized by a more massive resistor to greatly increase theefficiency of the element, as it is well known that there is adefiniterelation between the area of the space available for the elementand the cross section of the resistor which can be employed for a givenvoltage and wattage,'and there is also a definite relation between thecross section ofthe resistor and the durability of the element at agiven A further serlous object to sheathed wire is that the singlestrand resistor is disposed along a line parallel to its support for adistance, such, -that'the ,difl'ei'ences in expansion between theresistor and support sc't up'strains on the resistor which. causefailure. I

-- I am also aware that heating elements,

A .known as tubular elements,

have been formed by introducing a long smral resistor into a metal tubeand insulating it from the tube with finely divided refractory material.This type of' heating element is also very difiicult and expensive tomanufacture as it is necessary to introduce the spiral r'e sister. andinsulating material into, the end of the tube. Due to the fact that theelement is in rod form, the ratio of emissivity to .cross section iscomparatively low and the heat diffusion is not as good as with thin,flat types of elements. of resistor involves a central core ofrefractory material ;whi 'ch-requires useful .space and material, andthe core absorbs heat from the resistor. Such units necessitate a highresistor temperature for a given rate of energy. input which tends toshorten their life and to limit the possible safe rate of energyinput.While this type of element may be massed into spiral orserpentincshapes, it is open to the same objection as stated in connection withsheathed wire, namely, a double wall of refractory material and metalcasing is interposed betweenadjacent convolutions or lengths of theresistor.

A heating element in the form of a solid cylinder has'also' been made;This type of element is formed by first coiling the resistor on a rigidrod then" inserting the same into a metal tube-and filling theintervening space between the tube and resistor wi'th finely dividedrefractory material.

This type of element ,cannot be shaped, and it emits heat from the*outer surface only. It will be obvious that many of the disadvantages,fpreviously set forth also apply to this type of heatingelement.

A fourth-type-of heating element;-'is procore, or other core having aninsulating film The spiral form duced by winding the resistor on a micaapplied thereto, then applying a.layer of.

mica insulation thereabout, and finally sheathing the element in metal.This type of insulation is not truly refractory and."

hence the element will not stand thermal abuse. The res stor is not inintimate contact wlth a heat receiving'material ;over

its entire surface and is susceptible to, oxi? dation. Inasmuch as suchfragile material I asmica is used for insulation, it will at once beapparent that .theseheating elements' cannot be bent or'shaped withoutgreat risk of damage tothe insulation which would result'in ultimatebreak down,

the chief objection to this type of heating unit being the inability ofmica or other less refractorv insulation to continuously withstand hightemperatures, as well as the lack of density of the element orconductive intimacy between the resistor, insulation and support.

In so far as I am aware, a relatively thin and light weight heatingelement consisting of a resistor enveloped in a highly compacted mass ofrefractory material and having a sheet metal casing applied thereto, hasnever been successfully produced, and it is the general object of thepresent invention to provide a novelclass of heating elements and aprocess for making the same wherein the resistor is completely envelopedin a highly compacted mass of refractory material, with thewholecontained in a sheet metal casing, and the elements in eachinstance having relatively thin walls and large ratio of surface area tomass, so that maximum heat emissivcly is obtainable.

Another object is to provide a novel class of heating elements which bynature of their construction and relatively thin walls and cross sectionmay be easily shaped to lie in intimate contact with the object to beheated and thereby obtain minimum resistance to transfer of heat fromthe element to the object.

Another object is to provide a class of heating elements of theaforesaid character which may be entirely enclosed in an imperforatesheet metal casing and thus afford ample protection for the resistoragainst moisture or other foreign matter, or where conditions permit maybe enclosed in a partially or wholly perforated metal casing so that thecasing and refractory material will form an interlock with each otherand add to the. rigidity of the elements to prevent warping and alsomaintain the integrity of the element and facilitate the displacement ofthe metal casing during the forming or shaping operation hereinafterreferred to.

A still further object is to provide a group of heating elements whichmay be adapted, by forming or shaping when necessary, to numerous uses,and which sliall be simple in construction, inexpensive to manufactureand which shall be highly etllcient and durable in operation.

\Vith these and other objects inview, the invention consists in thevarious novel features of construction and arrangement or combination,all of which will be fully described hereinafter and pointed out intheappended claims.

In the accompanying drawings wherein I.

have shown various illustrative embodiments of my invention but Withoutintent to limit myself thereto, Fig. 1 is a plan View of a strip from anelement with parts broken away to more clearly show-the construction;Fig. 2 is a side elevation thereof with parts broken away; Fig. 3 is anenlarged trans-v verse section of the element shown in Figs. 1 and 2;Fig. 4 is an enlarged fragmentary view of a slightly modified form ofelement; Fig. 5 is a fragmentary plan view of a perforated coveremployed in some instances; Figs. 6 and 7 are side elevations of anelement such as shown in Figs. 1 and 2 and showing the same bent intotwo dilferent forms; Fig. 8 is a plan View of an irregularly shapedplate illustrating another form of my invention; Fi 9 is a sectionalview taken on the line 9-9 of Fig. 8; Fig. 10 is a side elevation of theplate showing the same bent into a suitable shape; Fig. 11 is a planview of a heating element in the form of a disk provided with aperforated casing; Fig. 12 is a sectional view through a dist: which hasbeen cupped; Fig. 13 is a plan view of a disk provided with animperforate casing; Fig. 14tis a plan view with parts broken away ofring type of element; Fig.

15 is a sectional View taken on the line 1515 of Fig. 14-; Figs. 16, 17and' l8 are plan views of modified forms of heating elements; Fig. 19 isa perspective view, with parts broken away, of a hollow cylindrical ty eof heating element; Fig. 20 is a longitu' inal view through acylindrical element; and Figs. 2l25 are sectional views showing thevarious steps in my process for forming the elements.

Referring particularly to Figs. l7 inclusive, wherein I have shown astrip type of heating element, 1 denotes the resistor wh ch ispreferably bent into serpent-inc form froma suitable resistance ribbon.This resistor is molded in and completely enveloped by a hard andcompact mass of cement like refractory material 2 which not onlysupports the ribbon at all points, due to its intimate contacttherewith, but also prevents oxidation of the resistor. Each end of theresistor is connected to a terminal 3 which may be of any suitable typebut prefcrably similar to that disclosed in my copending applicationSerial No. 555,870,

filed Apr-i121, \1922. These terminals are each provided with aninsulating washer i which prevent contact of the terminals with a sheetmetal casing composed of a channel receptacle 5 and a cover. plate 6which completely surround the refractory material. The side edges 7ofthc receptacle are deflected over the cover plate as clearly shown inFigs. 1 and 3, and the ends of the casing, beyond the terminals 3 areflattened as indicated at 8 and are provided with apertures 9 so thatthe element may be conveniently supported on a frame or fastened to anobject to be heated. If desired the seam formed by deflecting the sideedges 7 over the cover plate may be welded, although for ordinaryconditions, folding over the edges under high pressure will provesufficient.

fractor'y material and easing together.

- evenly distributed during the bending and A strip heating element ofthis general character is very thin, light in weight, and permitsmaximum transfer of heat from the resistor to the object to be heated.The resistor is completely enveloped in a compact mass of refractorymaterial and hence is supported at all points and is completelyprotectedagainst oxidation. These strips may be readily bent to various shapes tomeet the particular requirements. In Fig. 4: I have shown the elementbent to assume an arcuate cross section while in Figs 6 and 7 I haveshown the element bent into U- shaped form and circular formrespectively. The U-shaped form is suitable for application to molds andsimilar uses, while the circular form mayv be conveniently applied toany circular object, as for example, a pipe or water heater. A bolt 12engaged. through apertures 9 serves to retain the element in position onthe object.

In Figs. 813 inclusive, I, have shown a second group of heating elementswhich are characterized by "having relatively large areas and very. thincross sections. These elements are intended to replace the spiral andserpentine t pes of heatingelements' which are forme by bending andmassing sheathed wire or similar straight elements. Figs. 8 and 9 showan example of a polygonal type of heating elementmonsistlng of a sheetmetal receptacle 13 which is provided with a perforated cover 14 so thatthe refractory material 15 will interlock therewith..

This type of element as well as those previously described may be bentinto various shapes, without damage to the element or any parts thereof,and as an example, I have shown one side thereof bent over at rightangles in Fig. 10. If desired the other side may also be bent asindicated in dot ted lines in this figure.

In Fi s. 11 and 12 I have shown a circular type of heatin element whichhas the entire casing 16 perfbrated so that the refractory material andcasing are bonded on all surfaces. This type of element may be cupped asshown in Fig. 12 so that the element will contact at all points with avessel or other object having a semi-spherical surface. The perforatedcasing permits the metal to be hence prevents buckling;

In Fig. 13 I have shown a circular type of heating element having animperforate. casing 17 and which is adapted for use on a casing wallsfrom buckling.

flat surface, or as an insert. Because of refractory material andcasing, I preferably. insert therethrough a plurality of eyelets 1.8which effectively tiethe casing and refractory material together andprevent the In Fig. 14' I have shown a ring type of heating element inwhich the receptacle 20 of the cas'ng is in the form of acircularchannel. The resistor-21 is completely enveloped in a compactmass of refractory material as in the types previously described. Acircular metal cover 22 is laid on top of the refractory material andthe inner and outer peripheral edges of the receptacle 20 are deflectedover the washer as shown 'in Fig. 15. This type of heating element issomewhat similar to that. shown in;Fig. 7 exceptthat the casing ispreviously -.-formed into a circle about, its edge; an element.

such as. shown in Fig. 14 is .capaliIe,-of assuming various shapes'asfor example the triangular form 25 shown in 16, or the an ular orV-shaped form 26ishown in Fig. 1 or a modified triangular form 27 suchas shown in Fig. 18. These forms adapt themselves to variousrequirements. The form shown in Fig. 18 for example being suitedparticularly for electric irons. In Figs. 19. and 20 I have shown ahollow cylindrical type of heating elementwhich is particularly usefulfor application to pipes or cylinderswhich are to be heated. Thiselement maybe conveniently formed by providin a circiimferentially woundresistor comp etely enveloped in a compact mass of refractory materialand then enclosing the same in a sheet metal casing comprising an outermetal tube 29 having inturned peripheral edges 30 and an inner metaltube 31 having out-turned peripheral edges 32. This type of elementemits heat from its inner and outer cylindrical surfaces and also fromthe ends and hence is very efficient.

In Figs. 21-25 inclusive, I have illustrated the various steps employedin my process for forming the heating elements herein'disclosed. Incarrying out this process I first provide a sheet metal receptacle andfill the same with a mass of receptive refractory material 36. Inextinsert into this refractory material, a previousl formed resistor"refractory material with the resistor and the receptacle. In the caseof heating elements which are to be provided with an imprforate casing Inext dry the partially formed element and then apply a cover plate andeither simultaneously or in separate opera.

' formed with a a perforated cover 38 before or after the preliminarycompacting operation tions deflect the edges of the receptacle over thecover plate and heavily compress the element. 7

In the case of elements which are to be perforated casing, I apply driedand baked either by an external source of heat or by energizing theresistor.

While so far as the present invention is concerned, I do not limitmyself to any particular kind or refractory insulating matcfacilitatesbedded, electrical heating elements by prorial, one class foundespecially suitable for the purpose is composed of magnesiumor aluminumoxide or zirconium silicate, either individually where possible or acompound of them, together when desirable with a binding material suchas clay, to give the ncessary plasticity during fabrication and toeffect homogeneity in the final product.

The resistor element may be enveloped in the refractory insulatingmaterial in accordance with my Patent Number 1,136,076, issued April 20,1915 entitled Process of producing electrical heating devices or inaccordance with my Patent Number. 1.398,-'

410, issued November 29, 1921 entitled Embedding process.

Manifestly the present invention greatly the production of sheated, em-

viding a compartively shallow open sided receptacle into which thegranular refractory insulating material and the resistor may be properlyplaced before the receptacle is closed, thus distinguishing from, andaffording marked advantages over, the tubular type of elementhereinbefore referred to. Having thus described my invention, what Iclaim is 1. As a new article of manufacture, an electrical heatingelement consisting of a resistor, a formed sheet metal sheath envelopingsaid resistor and spaced therefrom, and a mass of grandular refractoryelectrical insulating material of high heat conducting quality fillingthe space between the resistor and the sheath, the resistor beingprovided with terminals each accessible through an opening in thesheath.

As a new article of manufacture, an electrical heating elementcomprising a resistor. a sheet metal sheath made up of a plurality ofparts enveloping said resistor and spaced therefrom, and a mass ofgranular refractory electrical insulating material resistor beingprovided each accessible through an opening in the 'a mass of grandularrefractory electrical 7 of high heat conducting quality filling thespace between the resistor and sheath, the with terminals sheath.

3. Asa new article of manufacture, an electrical heating elementconsisting of a resistor, a formed sheet metal sheath enveloplng saidresistor and spaced therefrom, andinsulating material filling the spacebetween the resistor and the sheath, the entire assembly being in ahighly compacted state, the resistor being provided with terminals eachaccessible througlran opening in the sheath.

4. As a new article of manufacture, an electrical heating elementcomprising a resistor arranged in flat formation, a sheet metal sheathmade up of a plurality of parts enveloping said resistor and spacedtherefrom, and an artificially compacted mass of .granular refractoryelectrical insulating material filling the space between the resistorand sheath, the resistor being provided with terminals each accessiblethrough i an opening in the sheath.

5. As a new article of manufacture, an electrical heating elementcomprising a resistor arranged in fiat formation, a sheet metal sheathmade up of a plurality of parts enveloping said resistor and spacedtherefrom, and an artificially compacted mass of granular refractoryelectrical insulating material filling the space between the resistorand sheath, said element having a relatively large area and a relativelythin cross section, the resistor being provided with terminals eachaccessible through an opening in the sheath.

6. As a new article of electrical heating element manufacture, ancomprising a resistor, a sheet metal sheath made up of a plurality ofparts enveloping said resistor and spaced therefrom, and an artificiallycompacted mass of granular refractory electrical insulating materialfilling the space between the resistor and sheath, the resistor beingprovided with terminals each accessible through'an opening in thesheath, said element having a relatively large area and a relativelythin cross section, the element being .capable of being formed to ashape other than fiat.

s a new article of manufacture, an electrical heating element comprisinga resistor, a sheet metal sheath made up of a plurality of partsenveloping said resistor and spaced therefrom, and an artificiallycompacted mass of granularre fractory electrical insulating materialfilling the space between 135 the resistor and sheath, said elementhaving a relatively large area and a relatively thin cross'section. theelement being capableof being formed to a shape other than flat and theresistor being of sinuous formation and arranged with its sinus in aplane substantially parallel to that of the relatively large area of theelement and being provided with terminals each accessible through anopening in the sheath.

, 8. As a new article of manufacture, an electrical heating elementcomprising a resistor, a sheet metal sheath enveloping said resistor andspaced. therefrom, the sheath comprised of parts that are held together;

by the marginal portion of one of said parts being turned over' themargin of the other, andan artificially compacted mass of granularrefractory electrical insulating material filling the space between theresistor and the sheath, the resistor being provided with terminals eachaccessible through an opening in the sheath.

9. As a new article of" manufacture, .an

electrical heating element comprising a resistor, a sheet metal sheathenveloping said' resistor and. spaced therefrom, the sheath beingcomprise of an open sided sheet metal receptacle and a cover appliedthereto and held to the rece tacle by the edge portion of the receptaclebeing turned over the edge of the cover throughout the peripherythereof, and an artificially compacted mass of granular-refractoryelectrical insulating material filling the space between the resistorand sheath, the resistor beingprovided with terminalseach accessiblethrough an opening in the sheath. u 4

11. As a new article of-'inanufact-ure,-an

electrical heating element comprising a sin y sheath.

uous resistor arranged in flat formation, a sheet metalfsheath made up.of a plurality of parts enveloping said resistor and spaced therefrom,and a mass of granular refractory electrical insulatingmaterial of highheat conducting quality filling the space between the resistor and thesheath, the sheath having a flat working face from which the resistor isuniformly spaced throughout its length, and the resistor being providedwith terminals each accessible through an opening in the sheath. 12. Anelectrical heating element comprising a sheath of sheet metal having apair of op osed superficial faces of comparatively arge area and a pairof faces connecting the former faces that are of comparatively narrowwidth, thesheath enclosing a shallow cavity, granular refractoryelectrical insulating material artificially compacted in said cavity,and a sinuous resistor enveloped in the insulating material and thesinus whereof lie in a surface which is parallel to the aforesaid facesof larger area, the resistor bein provided with terminals eachaccessible t irough an opening in the sheath.

13. As. a new article of manufacture, an electrical heating elementcomprising a resistor 'a sheet metal sheath made up of a plurality ofparts enveloping said resistor and spaced therefrom, a mass of granularrefractory electrical insulating material filling the space between theresistor and sheath, the resistor bein provided with terminals eachaccessible tirough an opening in the sheath, and means for tyin theopposit-e walls of said sheath toget er to prevent warping thereof, saidmeans being locatedwithin the area of the active surface of the element.v

-14.As a new article of manufacture, an electrical heating elementcomprising a-re-c sistor a sheet metal sheath made up of a plurality ofparts enveloping said resistor and spaced therefrom, and a mass ofgran-- ular refractory electrical insulating material filling the spacebetween the resistor .of the active surface of the element, and

the resistor ,beipg provided with terminals each'access'ible through anopening in the In testimony whereof, hereunto aflix mysignature. k

EDWI L, WIEGAND.

and the sheath, theopposite walls of said DBSOLAIMER l,614,330.1'5dwiaL. l Viegand, Dormont Borough, Pa. ELECTRICAL HEATING ELEMENT. Patentdated January 11, 1927. Disclaimer filed November 2, 1938, by thepatentee; and the licensee, Edwin L. Wiega'ad Company.

Herebyenter this disclaimer:

A.- To so much of claim 1 of said Letters Patent as may cover anyelectrical heating element in which the sheath surrounding the resistoris not relatively thin and wide in cross section, or does not constitutea surface of relatively large area for the transfer of the heat from theelement, or does not define a relatively shallow cavity of relativelysmall capacity, or in which the resistor is not arranged in a formationcorrespondingly relatively thin and wide in cross section, or in whichthe electrical insulating material is not compacted, or in which no partof the electrical insulating material is integrated into formationpositively spacing the resistor from the sheath.

B. To so much of claim 3 of said Letters Patent as may cover anyelectrical heating element in which the sheath surrounding the resistoris not relatively thin and wide in cross section, or does not constitutea surface of relatively large area for the transfer of the heat from theelement, or does not define a relatively shallow cavity of relativelysmall capacity, or in which the resistor is not a resistance conductorarranged in a formation correspondingly relatively thin and wide incross section, or in which the electrical insulating material is not ofhigh heat conducting quality, or in which the electrical insulatingmaterial is not in heat-conduction contact both with all parts of thesurface of said conductor over substantially the entire length of saidconductor and with all parts of the interior of the sheath surroundingthe resistor and adapted to conduct the heat generated in the resistorarranged in said relatively thin and wide formation substantially fromall parts of the surfa e thereof readily and directly to all parts ofsaid relatively large area heat-transfer surface, or in which no part ofthe electrical insulating material is in integrated condition anddisposed in position positively spacing the resistor from the sheath. ClTo so much of claim 5 of said Letters Patent as may cover any electricalheating element in which the electrical insulating material is not ofhigh heat conducting quality, or in which the sheath surrounding theresistor is not relatively thin and wide in cross section, or does notconstitute a surface of relatively large area for the transfer of theheat from the element, or does not define a relatively shallow cavity ofrelatively small capacity, or in which the resistor is not a resistanceconductor arranged in a formation correspondingly relatively thin andwide in cross section, or in which the electrical insulating material isnot in heat-conduction contact both with all parts of the surface ofsaid conductor over substantially the entire length of said conductorand with all parts of the interior of the sheath surrounding theresistor and adapted to conduct the heat generated in the resistorarranged in said relatively thin and wide formation substantially fromall parts of the surface thereof readily and directly to all parts ofsaid relatively large area heat-transfer surface.

D. To so much of claim 12 of said Letters Patent as may cover anyelectrical heating element in which the electrical insulating materialis not of high heat conducting quality, or in which the sheathsurrounding the resistor is not relatively thin and wide in crosssection, or does not constitute a surface of relatively large area forthe transfer of the heat from the element, or does not define arelatively shallow cavity of relatively small capacity, or in which theresistor is not a resistance conductor arranged in a formationcorrespondingly relatively thin and wide in cross section, or in whichthe electrical insulating material is not in heat-conduction contactboth with all parts of the surface of said conductor over substantiallythe entire length of said conductor and with all parts of the interiorof the sheath surrounding the resistor and adapted to conduct the heatgenerated in the resistor arranged in said relatively thin and wideformation substantially from all parts of the surface thereof readilyand directly to all parts of said relatively large area heat-transfersurface.

[Ofiicial Gazette December 6', 1.938.]

